A high-gain harmonic-generation free-electron laser is demonstrated. Our approach uses a laser-seeded free-electron laser to produce amplified, longitudinally coherent, Fourier transform-limited output at a harmonic of the seed laser. A seed carbon dioxide laser at a wavelength of 10.6 micrometers produced saturated, amplified free-electron laser output at the second-harmonic wavelength, 5.3 micrometers. The experiment verifies the theoretical foundation for the technique and prepares the way for the application of this technique in the vacuum ultraviolet region of the spectrum, with the ultimate goal of extending the approach to provide an intense, highly coherent source of hard x-rays.

We report the first experimental results on a high-gain harmonic-generation (HGHG) free-electron laser (FEL) operating in the ultraviolet. An 800 nm seed from a Ti:sapphire laser has been used to produce saturated amplified radiation at the 266 nm third harmonic. The results confirm the predictions for HGHG FEL operation: stable central wavelength, narrow bandwidth, and small pulse-energy fluctuation.

We report on an experimental investigation characterizing the output of a high-gain harmonic-generation (HGHG) free-electron laser (FEL) at saturation. A seed CO2 laser at a wavelength of 10.6 microm was used to generate amplified FEL output at 5.3 microm. Measurement of the frequency spectrum, pulse duration, and correlation length of the 5.3 microm output verified that the light is longitudinally coherent. Investigation of the electron energy distribution and output harmonic energies provides evidence for saturated HGHG FEL operation.

The DUVFEL electron linac is designed to produce sub-picosecond, high brightness electron bunches for driving a short wavelength FEL. Four experiments have been commissioned to address the challenge of accurately measuring bunch lengths on this timescale. In the frequency domain, a short 12 period undulator is used to produce both off-axis coherent emission and on-axis incoherent single-shot spectra. The total coherent infrared power scales inversely with bunch length and the spectral cutoff is an indication of bunch length. The density of power spikes in the single-shot visible spectrum may also be used to estimate bunch length. In the time domain, the linac accelerating sections and a bending magnet are used to implement the RF-zero phasing method, and a subpicosecond streak camera is also installed.Beam measurements and comparisons of these methods are reported. RF ZERO PHASINGThe RF zero phasing method [1] uses the accelerator itself as a relativistic streak camera. A large timecorrelated energy spread (linear chirp) is induced on the beam by setting the phase of one or more linac sections to

A short-period in-vacuum undulator for the NSLS X-ray Ring has been developed in a collaboration between SPring-8 and the NSLS, and has achieved its project design goals during commissioning studies. The device is called IVUN (in-vacuum undulator) and employs magnet arrays (31 periods, with an 11 mm period) developed at SPring-8, while the requisite vacuum chamber and mechanical systems were developed at the NSLS. At a magnet gap of 3.3 mm, IVUN produces 4.6 keV radiation in the fundamental, with useful photon fluxes in both the second and third harmonics. The magnet gap is adjustable between 2 and 10 mm. A brief overview of IVUN is presented, together with initial commissioning results: the dependence of electron-beam lifetime and bremsstrahlung on magnet gap, and the output radiation spectrum.

Abstract-qW e report on the first lasing of a high-gain harmonic generation (HGHG) free-electron laser (FEL). The experiment was conducted at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL). This is a BNL experiment in collaboration with the Advanced Photon Source (APS) at Argonne National Laboratory. A preliminary measurement gives a high-gain harmonic generation (HGHG) pulse energy that is 2X107 times larger than the spontaneous radiation, In a purely self-amplified spontaneous emission (SASE) mode of operation, the signal was measured as 10 times larger than the spontaneous radiation in the same distance (-2 m) through the same wiggler. This means the HGHG signal is 2X106 times larger than the SASE signal. To obtain the same saturated output power by the SASE process, the radiator would have to be 3 times longer (6 m).

A high-flux insertion device and beamline for macromolecular crystallography has been built at the National Synchrotron Light Source (NSLS) that employs a mini-gap undulator source developed by the NSLS. The mini-gap undulator at beamline X29 is a hybrid-magnet device of period 12.5 mm operating at proven gaps of 3.3-10 mm. The beamline provides hard X-rays for macromolecular crystallography experiments from the second and third harmonics over an energy range of 5-15 keV. The X-ray optics is designed to deliver intense and highly collimated X-rays. Horizontal focusing is achieved by a cryogenically cooled sagittally focusing double-crystal monochromator with approximately 4.1:1 demagnification. A vertical focusing mirror downstream of the monochromator is used for harmonic rejection and vertical focusing. The experimental station hosts an Area Detector Systems Quantum 315 CCD detector with 2.2 s readout time between exposures and Crystal Logic goniostat for crystal rotation and detector positioning. An auto-mounter crystal changer has been installed to facilitate the high-throughput data collection required by the major users, which includes structural genomics projects and the Macromolecular Crystallography Research Resource mail-in program. X29 is 10(3) times brighter than any existing bending-magnet beamline at NSLS with an actual flux of 2.5 x 10(11) photons s(-1) through a 0.12 mm square aperture at 11.271 keV.

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